The present invention relates to a method for fabricating a semiconductor device and, more particularly, to a method for forming a polycrystalline silicon film or a polysilicon film.
A polysilicon film is essential to a semiconductor device. For example, the polysilicon film is used for an electrode of a capacitor provided in an insulating film covering a semiconductor substrate or conductive material for filling a contact hole provided in the insulating film. In that case, the polycrystalline silicon film is required to be deposited on a step portion of the insulating film made by the capacitor or the contact hole. The polysilicon film is further required to dope impurities therein to lower the resistivity thereof.
In order to decrease the steps in fabrication, it was reported in "JAPANESE JOURNAL OF APPLIED PHYSICS", vol. 23, No. 7, Jul. 1984, pp. L482-L484, that an impurity doping gas is introduced during the growth of the polysilicon film. The polysilicon film is thus grown on the step portion of the insulating film while doping impurities thereinto. This method is called hereinafter "in situ doping method".
However, the so-called step coverage of the doped polycrystalline silicon film thus made is very poor, so that the deviation of the capacitance value becomes large and the contact resistance value is made high.